1. Field
The present invention relates to tether system for a safety line, particularly for a fall arrest system.
2. State of the Art
Prior art safety systems are known in which tall structures are fitted with a safety systems such as self retracting lifelines (SRLs) anchored at an elevated position on the structure. For example towers, masts, or wind turbine structures may be fitted with a SRL anchored at an elevated position toward the top of the structure. A personnel ladder is typically secured to the structure to enable personnel access to the top of the structure for maintenance or other purposes. The person secures themselves to the SRL before climbing the ladder and following ascent and subsequent descent of the ladder the person releases the SRL.
There is an issue that the SRL, when not in use, as the line in the retracted position is wound onto the SRL drum in the housing of the SRL. This ensures that the safety line is not exposed when not in use. However it means that when the person is at the foot of the structure before ascending the ladder, the attachment point at the end of the line is positioned high up at the SRL.
There are various solutions to this problem. In a first prior art system the attachment point (karabiner) at the end of the safety line is secured to an endless tether line loop mounted about a pair of pulleys one positioned at the foot of the structure and one high up toward the top of the structure. The tether line loop can be pulled by a person positioned at the foot of the structure and as the tether line moves along its path the end of the safety line connected to the tether line is pulled downwardly in so doing paying out the safety line from the SRL. When the end of the safety line is pulled down all the way to the foot of the structure the person can secure the safety line to their personal harness for ascent of the structure. Following descent, the person can unclip the safety line from the harness and ensure hat it is re-secured to the tether line. The person can then pull the tether line in the reverse direction to allow the safety line to retract back into the SRL.
In the hostile maritime environment the pulley wheels and line arrangement can become corroded and seized and therefore inoperable. Also there are problems in tensioning such systems in conditions of strong tides and powerful waves.
An alternative solution is shown in for example WO2007/128307. In this arrangement an auxiliary line is connected to the end of the safety line. When the safety line is fully retracted into the SRL housing, the length of the auxiliary line extends downwardly by a distance equivalent to the height of the structure. The user at the foot of the structure pulls on the auxiliary line in order to pull the SRL attachment karabiner downwardly paying out the safety line for attachment to the user. A disadvantage is that the auxiliary line may become tangled making subsequent automatic retraction of the safety line into the SRL difficult. If the safety line is not fully retracted following use the internal parts of the SRL may be left open to corrosion as would be the length of safety line remaining exposed.
An improved tether and safety system has been devised which provides advantages over known prior art systems.
According to the present invention, there is provided a tether system for a safety line, the tether system comprising:                an elongate guide track;        a plurality of stay elements arranged to move along the guide track and be carried at spaced positions along the length of a tether line.        
It is preferred that the system includes a tether line for connection to the safety line.
The elongate guide track is preferably provided with bracket fixing means for mounting the guide track, proximate opposed ends, to a structure.
In certain embodiments, it may be preferred that the elongate track is mounted in tension. In such an embodiment, it may be preferred that the system includes a tensioning arrangement for imparting, or varying, tension into the elongate guide track.
In certain embodiments the guide track may comprise a flexible elongate line such as a length of webbing, ribbon, cable or rope.
It is preferred that the guide track is a fixed position guide track, As opposed to a moving pulley system, for example.
It is preferred that the stay elements include a formation arranged to permit sliding travel with respect to the track element whilst inhibiting parting or separation of the stay elements and guide track.
The stay elements may include a channel or slot formation arranged to permit sliding travel with respect to the track element.
It is preferred that the stay elements are provided with means for securing to the tether line. For example the stay elements may be provided with holes through which the tether line extends for securing. The holes may be dimensioned such that the stays do not slide along the tether line, but rather are secured in position and move with the tether line.
Typically the elongate guide track is oriented substantially vertically.
Typically, the elongate guide track is mounted to or adjacent to a ladder structure.
According to a related aspect, the invention provides a fall arrest or protection system mounted to a structure, having an ascent/descent ladder fixed to the structure, the system including a self-retracting safety line device including a safety line, mounted at height; an elongate guide track extending along at least a part of the length of the ladder; a plurality of stay elements arranged to move along the guide track and be carried at spaced positions along the length of a tether line connected to the safety line.
The invention will now be further described, by way of example only, with reference to the accompanying drawings.